Everyone has heard
the phrase, "Don't throw out the baby with the bath water."
But do dog breeders ever stop to consider how this admonition applies
to them? Certainly not the novice who righteously declares that he
will never, ever, keep anything that has even the possibility of
producing the smallest genetic defect. Not even the experienced
breeder who refused to consider an otherwise excellent line because
it sometimes throws cataracts. This tendency toward genetic over-kill
not only culls dogs that might have something to offer, it can
exacerbate the very problems breeders are trying to avoid. The
following is a real life example of what can happen when breeders
exercise short-sighted culling in the name of genetic disease control.

About twenty years
ago, breeders of Basenjis launched a campaign to wipe out a fatal
genetic disease called pyruvate kinase deficient hemolytic anemia
(HA). HA is caused by a recessive gene. Dogs with a single copy of
the gene are healthy, but those with two copies die. A screening test
was developed that would indicate carriers as well as affected
animals. Breeders zealously screened their dogs, eliminating not only
affected animals, but the healthy carriers from the breeding population.

Today HA is rare
in Basenjis, but the incidence of Progressive Retinal Atrophy is
significantly higher. As is yet another fatal disorder, a kidney
problem called Fanconi's Disease. Neither of these diseases had a
screening test that would indicate carriers. Had breeders been less
fanatical in their pursuit of HA, they might have retained the
healthy carriers in the breeding population, breeding them only to
non-carriers so they could avoid producing HA-affected puppies. By
such a method they could have retained the good aspects of those
carriers, including freedom from genes for PRA or Fanconi, while
gradually lowering the incidence of the HA gene.

Fortunately for
the Basenji, there is still a native population of the breed in
Africa. The Basenji club prevailed upon the AKC to allow them to
re-open the stud book to admit some African-born Basenjis. This badly
needed source of new genetic material comes at great trouble and
expense for those breeders who make the effort to acquire one of
these imports. This option isn't even possible in some breeds, and
even where it is, convincing a large registry like AKC to accept
undocumented foreign imports is itself a daunting task.

In spite of what
happened with the Basenji, this should not be viewed as an indictment
of screening tests. The problem wasn't the HA test, but the drastic
culling process that breeders undertook when using it. If there is a
test which can identify carriers, make use of it. Breeders need to
know as much as possible about the genetic potential of their
breeding stock. Ideally, they should be willing to share the results,
whether good or bad, with other breeders.

Knowledgeable dog
people know there is no perfect dog. Even the best of them have
faults. The faults are not only those conformation or behavioral
problems you can readily observe, but also bad genes. Dogs have at
least 80,000 genes. No matter how high the standards for selection of
breeding stock or how strict the culling of offspring, every dog will
have genes for unwanted traits. Experts agree that every individual
"be he dog, human or cauliflower" probably carries three
"lethal equivalents." This may leave you wondering why we
aren't seeing dogs and cauliflowers, not to mention each other,
dropping like flies all around us.

Under normal
circumstances, lethal genes remain rare. Natural populations breed
randomly, maintaining a varied mix of alleles, or forms, of genes.
Only occasionally will the right combination of bad alleles match up
to produce an affected individual. In addition, the lethal nature of
these diseases limits the ability of affected animals to pass them on
to their offspring because affected individuals often don't live long
enough to reproduce. But the breeding of purebred livestock,
including dogs, is not natural or random. It is selective based on
the wants and needs of breeders. As a result, the number of lethal
equivalents in most breeds exceeds the average of three, the problem
genes having been inadvertently concentrated through the standard
inbreeding practices used to maximize production of desired traits.
Two examples in Australian Shepherds are Pelger-Huet Anomaly and
merle. Genes with lethal effects are only the tip of the iceberg.
There are dozens, if not hundreds, of genes whose effects are
anywhere from minor to extremely bad.

Breeders routinely
evaluate breeding stock by studying conformation and/or performance
attributes in minute detail. Virtues are weighed against faults, then
compared to the virtues and faults of prospective mates. If the
overall analysis is positive, the breeder will proceed. Hereditary
diseases and defects need to be given the same kind of consideration,
in and of themselves and in combination with all the dog's other traits.

Some faults are
severe enough to eliminate a dog from breeding consideration
entirely, but even genetic defects and disease may not necessarily
fall into this category, in some circumstances. Remember the case of
the Basenjis and HA. Dogs proven to be carriers of traits in which
only homozygotes (those with two copies of the gene) are affected,
can be used if care is taken never to mate one carrier to another and
not to use them extensively.

If the mode of
inheritance for a trait is unknown or polygenic, identifying carriers
can be difficult. Individuals which repeatedly produce traits like
hip dysplasia, epilepsy or thyroid disease should be pulled from
further breeding because of the serious and debilitating nature of
those diseases. But their relatives may be used if care is taken to
select mates unlikely to carry the same defect. If at any point an
individual proved to be a repeat producer of the defect, it could
then be removed from the breeding program.

Many faults are
variable in expression. This includes such genetic defects as hip
dysplasia (HD) and missing teeth. In Clumber Spaniels, where HD was
once almost universal, elimination of all affected animals was not an
option if the breed was to be preserved. By selecting away from the
most severely affected dogs, Clumber breeders have managed to improve
their overall situation, producing more non-dysplastic dogs and fewer
which are severely affected, even though HD is still common. A
similar situation has occurred with Collies and Collie Eye Anomaly.

In the case of
missing teeth, a fault common in Australian Shepherds, something
similar could be done. There are sufficient quality dogs with full
dentition that dogs missing multiple teeth ought not to be bred.
However, those missing one or two could be bred to mates with full
dentition out of families with full dentition. If breeders were
conscientious about screening and mate selection, none of the good
traits those dogs have need be lost along the way.

The overall size
of a breeding population must be taken into account before making
final decisions on whether a dog exhibiting or carrying a defect
ought to be bred. Australian Shepherds are numerous, but certain
sub-sets of the breed are not. In North America there are thousands
of Aussies, but in other parts of the world populations typically
number only a few hundred breeding animals at best. Opportunities to
add new stock are infrequent, especially in those countries with
strict quarantine laws and import restrictions. Even in North America
a breeder's selection of potential mates may be limited if his
breeding goals are very specific, such as producing a particular type
of stock dog.

In small
populations, breeders may have no choice but to use some defective
animals. The only alternative is increased inbreeding which will
narrow the available gene pool even further, bringing other, possibly
worse, defects to the fore. If defective dogs are to be used,
breeders must avoid subsequent inbreeding on those dogs. Neither
should such a dog be bred extensively. Among its offspring, only
those which do not exhibit the defective trait should be considered
for further breeding.

If breeders
approach genetic disease with an objective eye and if they are honest
with themselves and each other about the potential for producing
genetic diseases and defects in any given cross, they can obtain
healthy babies while the bath water full of bad genes drains slowly away.